The National Fire Protection Association has released its annual report on firefighter fatalities in the United States, and a leading cause of on-duty deaths in the fire service remains cardiac issues despite those deaths hitting an all-time low in 2016.

Last year’s total of 69 on-duty deaths marked the fifth time in six years that the number was below 70, according to the NFPA’s 2016 Report.

The 26 deaths attributed to cardiac issues marked the fewest since the NFPA began this study in 1977, but it was still high enough to match internal trauma as a leading cause. Sudden cardiac death has consistently been the leading cause for on-duty deaths year in and year out in the NFPA’s study.

Of the 69 total deaths, 39 were volunteers, 19 were career firefighters, eight were employees of federal land management agencies, one was a contractor with a state land management agency, one was a member of an industrial fire brigade and one was a prison inmate.

“When NFPA began reporting on firefighter deaths 40 years ago, the annual average was close to 150 fatalities per year,” Rita Fahy, NFPA’s manager of fire databases and systems, said in a release. “Over the past five years (between 2012 and 2016), the annual average has dropped to less than half that at 73 deaths, so we’ve clearly seen a significant decline in on-duty firefighter fatality rates over time.”

The number of deaths attributed to cardiac issues dropped starkly from 51 percent in 2015, while the increase in internal trauma deaths — which was 24 percent in 2015 — could be attributed in part to deaths related to vehicle accidents jumping from 12 percent in 2015 to 25 percent last year.

Although the report has consistently shown a decline in on-duty firefighter fatalities in recent years, the NFPA is quick to point out that this does not provide the full picture of the risks firefighters face even years after the job — particularly with the issues of job-related cancers and PTSD coming to the forefront in the industry.

“While the annual report accurately reflects steadily declining rates among on-duty firefighters,” Fahy said, “it doesn’t capture many of the deaths that occur off duty that are ultimately the result of on-duty activities.”

Lawrence Matthews died doing what he loved. The dedicated Dolton firefighter collapsed Saturday afternoon while battling a fire in neighboring Harvey.

Matthews went into cardiac arrest and was taken to Ingalls Memorial Hospital, but never regained consciousness, and was pronounced dead at 3:15 p.m.

Chicago and suburban police officers and firefighters saluted the ambulance carrying Matthews’ body in a solemn procession to the Cook County Medical Examiner’s office.

Matthews, 35, was a husband and father of four, who had been with the Dolton Fire Department since 2009.

Dolton firefighters had been called in to assist the Harvey Fire Department on Saturday, after multiple mobile homes caught fire near 150th and Maplewood. Officials said Matthews was on the sidewalk after arriving at the scene when he went into cardiac arrest.

Matthews was a heart transplant recipient who had defied the odds to become a firefighter. Just two years after he received his new heart at the University of Chicago Hospital, Matthews became a firefighter with the blessing of his doctors.

An autopsy of a Dolton firefighter who died in the line of duty was performed Sunday, but a determination for the cause of his death was still pending, according to the Cook County medical examiner’s office.

Firefighter Lawrence Matthews, 35, of Glenwood, collapsed and went into cardiac arrest after battling a blaze at a mobile home Saturday in Harvey. He was transported to Ingalls Memorial Hospital, and pronounced dead at 3:15 p.m.

Matthews was the recipient of a heart transplant in 2007 at the University of Chicago Hospital. Doctors approved his working as a firefighter after he passed a physical, and in 2009 he was sworn in.

The mobile home near 150th Street and Rockwell Avenue was destroyed in the fire.